So many LTE bands! Why?

Did anyone notice the T-Mobile version has more LTE bands than most of the other carriers' models.
1/2/4/5/7/17 for T-Mobile and AT&T only has 1/4/7/17. Band 2 makes sense to me, since eventually T-Mobile will have to use some of their 1900 Mhz spectrum for LTE, but why band 5? T-Mobile doesn't own any of that, but AT&T, who had a ton of it, doesn't have the band. It makes me wonder if T-Mobile is hoping to buy up some 850 Mhz from a regional carrier.

Very simple. Carriers around the world are using different LTE bands. Specifically T-Mobile in Europe is using the 2600 band, so if you want to get a local SIM when traveling for high speed data you need those bands. That's why I want to buy the T-Mobile branded phone as opposed to all the others.